#include "AUD_LowpassCalculator.h"

#include <cmath>

#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif

AUD_LowpassCalculator::AUD_LowpassCalculator(float frequency, float Q) :
	m_frequency(frequency),
	m_Q(Q)
{
}

void AUD_LowpassCalculator::recalculateCoefficients(AUD_SampleRate rate, std::vector<float> &b, std::vector<float> &a)
{
	float w0 = 2 * M_PI * m_frequency / rate;
	float alpha = sin(w0) / (2 * m_Q);
	float norm = 1 + alpha;
	float c = cos(w0);
	a.push_back(1);
	a.push_back(-2 * c / norm);
	a.push_back((1 - alpha) / norm);
	b.push_back((1 - c) / (2 * norm));
	b.push_back((1 - c) / norm);
	b.push_back(b[0]);
}